The present invention generally relates to a method and apparatus for detecting the presence of rock during coal or ore mining operations.
A more effective way to control solid mineral mining equipment, or miners, has been greatly desired by the mining industry. Many concepts have already been tried, over a period of many years, to improve mining controls to increase the amount of coal, or other mineral, cut by the mining equipment and to decrease the amount of undesirable rock cut by the mining equipment. Many of these concepts involve xe2x80x9cguidancexe2x80x9d systems that direct or point the miner where to cut, based on predictions or assumptions related to the location of the mineral-rock interface. These predictions or assumptions are typically based on data or information obtained from the experience of the mining equipment from previous cuts.
One seemingly simplified approach employs repetitive cycles. A computer is instructed by the miner operator to perform specific cycles or the control system is programmed to memorize operator actions over a cycle and duplicate them. This approach does not work well because of the high variability of the rock and mineral formations and operational considerations. This approach is particularly ineffective when applied to continuous miners, because the miner rides on the floor that has been cut resulting in cutting errors (e.g., leaving an excessive layer of coal on the floor, or cutting excessively down into the rock on the floor) for one cut tending to be amplified for subsequent cuts.
In the case of long-wall mining there is some opportunity to utilize what has been learned on one pass along the mineral face to improve upon cutting strategy for the next pass along the face. One approach utilizes a memory system to log the profiles of the rock face at the floor and roof on one pass and then to use this knowledge to influence the cutting as the cutters pass along the same face, going in the opposite direction. This approach has been of only limited success because the rock face profile on one pass does not exactly reflect the needed rock face profile of the next pass and because there is much variability in the formations and mining operations. Consequently, such equipment and operation are limited in their efficiency in cutting to the rock-coal interface using guidance strategy.
Gamma detectors have, over the years, shown promise in detecting the location of the rock-wall interface for both continuous miners and long wall miners, but typically have not been effective because they have been installed so as to measure where the mining equipment has been rather than where the cutter is going. One reason that gamma detectors have often been used in a non-effective manner is that the detectors could not physically survive if subjected to the environment in locations where they would be most effective.
Numerous other approaches have already been conceived and tested over the years for directing or guiding mining equipment. Most of these concepts have not proven to be commercially successful due to technical deficiencies, implementation problems, and cost. Many types of sensors have been incorporated into control systems to monitor the shape, profile and characteristics of the formations through which the mining equipment is cutting and to make cutting decisions on where to point subsequent cuts based on this information. Thus, these approaches fail not only due to practical implementation problems but also because of a fundamental flaw with the concept. Knowledge about the shapes, profiles, or characteristics of the formation being passed through does not provide accurate information about the formation just ahead, for which the cutting decisions must be made.
In most of the examples above, the control systems employed have been complex and expensive. A typical approach is to use a gravity-referenced or inertial-referenced control system, with various other sensors added. Some of these control concepts have been referred to as xe2x80x9chorizon control systems.xe2x80x9d A horizon control system typically uses the gravity-referenced sensors or inertial-referenced sensors that keep track of the orientation of the continuous miner and the profile of the roof and floor.
In principle, the horizon control system approach is to control the mining equipment by use of guidance systems adapted to mining applications. However, as discussed above, guidance systems cannot generate accurate information about the formation to be cut because the historical information that they log in detail is not a valid indicator of what is ahead. Moreover, these guidance systems are complex and costly.
It is described in co-pending U.S. application Ser. No. 09/811,781 that in underground coal mining, a properly designed and properly positioned, forward-looking armored gamma detector, in combination with a suitable control system; can be effective for reducing the amount of rock taken while extracting an increased amount of coal or other mineral. A mining control system that incorporates such forward-looking detectors is referred to as a xe2x80x9crock avoidance system.xe2x80x9d The use of rock avoidance systems can help cut the floor of the mine very smoothly and simplify the job of the operator. Rock avoidance systems allow continuous miner operators to be positioned further from the coal face, thus reducing health hazards.
However, even when used with forward-looking rock detectors as described in co-pending U.S. application Ser. No. 09/811,781, these horizon control systems do not utilize the data generated by the rock detectors as fully as it could be used, because the systems are conceived and designed to guide or point, determining the direction to move, rather than being appropriately responsive to sources of external intelligence such as armored gamma detectors. In addition, inertial or gravity referenced systems are not typically designed to provide precision and timely measurements of cutter movements that will allow a rock detector to achieve maximum sensing accuracy.
Rock avoidance systems that rely upon complex guidance systems are costly and, complicated and have some inherent inefficiency resulting from their methodology. A need now exists to provide an accurate rock avoidance system that is simple, economical and easy to install and operate. There is also a need for such a rock avoidance system for use on long-wall mining equipment as well as continuous mining equipment.
These deficiencies are alleviated to an extent by the present invention which in one aspect provides a rock avoidance system for solid mineral mining using a forward looking rock/mineral interface detector and controlling the miner to cut to the detected rock/mineral interface.
In another aspect, vertical movements of the cutting mechanisms are measured for the purpose of being used by the rock detector to make more accurate mathematical calculations of the location of the coal-rock interface.
In another aspect, a method is provided for improving accuracy by incorporating a device within an armored rock detector to sense angular movements of the cutter boom and to correlate changes in gamma radiation to the angular movements, within selected energy ranges. An armored rock detector, so configured, can make effectively accurate cutting decisions under a wide range of mining conditions without support from complex control systems. Cutting decisions from the rock detector are transmitted directly to the miner control system to slow or stop the movement of the cutter toward the coal-rock interface or to a control and display panel where other constraints and logic may be applied.
In another aspect, the change in attenuation is determined, and the thickness of the remaining coal is calculated by measuring the rate at which the gamma radiation increases. Greater accuracy in the calculations is achieved by measuring the relative changes in gamma counts for various energy levels. Quick response is achieved so that the cutter of a continuous miner moving toward the rock on each cut may be stopped before reaching the rock by employing curve-fitting techniques that correlate the gamma ray measurements with incremental movements of the cutters. The rock detector is outfitted with the required logic elements and algorithms.
In yet another aspect, a method of geosteering is provided on a continuous miner is for a shearing down to be slowed slightly as the floor is approached. Control of the shearing is accomplished by signals from the rock detector which operate the solenoids that control the hydraulic system. Following the shearing stroke, the miner is placed in reverse for a short distance in order to remove the small cusp left behind the cutter. During this backing up, the rock detector will maintain the boom at constant angle so that the floor will be cut level. Next, the operator moves the miner forward slowly, simultaneously shearing up, to sump to approximately fifty percent the diameter of the cutter. If a rock detector is used at the roof, it will slow the cut slightly before reaching the rock interface and then stop the cut. While the boom is being held at a constant angle by the rock detector, the operator drives the miner forward to a full sump. At this point, the operator is ready to start the shear down to repeat the cycle.
In another aspect, the rock detector is placed near the cutter on a continuous miner, so that it can detect the radiation passing through the coal in front of the advancing cutter. When cutting at the floor, the detector moves with the advancing cutter such that the angular size of the field of view is not reduced as the cutter moves down toward the bottom portions of the miner.
In another aspect, the rock detector is placed near the cutter on a long-wall miner When geosteering the trailing drum, the divergence rock detector is positioned within a few feet of the bottom edge of the picks so that a divergence between the tips of the picks and the rock will be detected before coal is left unmined. Also, the divergence rock detector is positioned close to the picks so that the cutter can be biased toward divergence without concern for leaving coal unmined. In another aspect, a convergence rock detector is used on the trailing drum, and positioned close enough to the cutter to be able to detect rock that is being mined and then mixed with the coal. In a preferred embodiment a geosteering system is provided that includes an armored rock detector, positioned on the boom of a continuous miner to view the area where coal is being cut, to measure the changes in gamma radiation as a result of the coal being cut away, to correlate the changes in gamma radiation with incremental changes in the position of the cutter, and to make logical decisions when to slow and/or to stop the cutter before cutting into the rock. In order to obtain precise measurements of rotation of the cutter boom or of the vertical movements of the cutter, an accelerometer is incorporated into the rock detector.
In another preferred embodiment, the geosteering system includes a control and display panel that keeps the operator informed about the cutting progress, particularly in regard to cutting at the roof. This panel accepts data and decisions from the rock detectors and also displays the position of the cutter relative to the most recent cuts at the floor. A solid-state accelerometer, in the form of a micro-chip, is included as part of the electronics. This accelerometer acquires additional information on the instantaneous motion of the continuous miner and sends that information to the rock detector so that the rock detector can subtract errors resulting from motion of the miner from the measured incremental movement of the cutter and rock detector. In a typical application, gamma data is correlated to the incremental movements of the cutter and this information is retained within the control and display panel for at least ten cutting cycles. Detailed, automatic analysis of this data allows refinement of the logical decisions to be made for future cutting cycles.
In another embodiment, an encoder and/or a potentiometer are provided to instantly measure and report to the rock detector, the movement of the boom, on which the cutter is attached. Such substantially instant, precise data allows the rock detector to make fast, accurate measurements. When rock detectors are being used for controlling cutting at the roof, in addition to controlling cutting at the floor, such auxiliary devices provide supporting information to the rock detector, to the miner control system, and to the operator. This preferred embodiment includes a cutter motion indicator, containing an optical encoder and a potentiometer, at the pivot point of the boom. By combining this precise, high-speed data with the expanded computational capabilities of other preferred embodiments, advanced automation at higher speeds of operation are made possible.
In yet another embodiment, rock detectors are used to steer the cutting of a long-wall mining system. In some applications, both the leading drum and the trailing drum of a long-wall shearing system are geo-steered by use of rock detectors. Whenever the mining equipment reverses direction, the leading drum becomes the trailing drum. The armored rock detector is placed near the bottom of the cowl for the trailing drum and allows direct view of the surface being cut by the drum. The rock detector begins by slowly raising the drum until the rock detector determines that coal is being left unmined. Raising and lowering of the drum by the rock detector is accomplished by operating the solenoids that control the hydraulic system. Upon recognition that a small amount of coal is being left over the rock, the rock detector quickly lowers the drum by approximately two inches. The amount that the drum is lowered will depend upon the miner and mining conditions. In one aspect, the rock detector continues to steer the drum so that the cutting operation cycles between three conditions (1) removal of only a small amount of rock, (2) preferable removal of all coal and no rock, and (3) leaving up to one or two inches of coal over the rock. In the case where the coal bonds well to the rock, typically fire clay, the maximum amount of coal occasionally left will preferably be less than two inches. The preferable result is that for most of the cut along the face, almost no floor rock is mined and very little coal is left unmined. For the case where soft coal is not bonded to the fire clay, preferably substantially all of the coal will be removed substantially all of the time.
These and other objects, features and advantages of the invention will be more clearly understood from the following detailed description and drawings of preferred embodiments of the present invention.